The invention relates to a method of packaging by wrapping, according to which method a top film is placed on top of an object being packaged and plastic film web used as packaging material is wrapped around the object being packaged, and which method involves the following stages:
a top film sheet of the desired size is cut from the top film web, which sheet is brought to the wrapping station to a position above the object being packaged,
during the first wrapping stage, plastic film web is wrapped around the object being packaged, preferably from bottom to top,
the edges of the top film sheet are turned downwards on top of the already wrapped plastic film layer,
and during the second wrapping stage, plastic film web is wrapped on top of the edges of the top film sheet.
The invention also relates to a wrapping machine for packaging the object being packaged with the top film and the plastic film web used for wrapping, the wrapping machine comprising:
a cutting device for cutting a top film sheet of the desired size from the top film web,
a device for bringing the top film sheet to the wrapping station, to a position above the object being packaged,
a wrapping device for wrapping the plastic film web around the object being packaged,
and a device for turning the edges of the top film sheet downwards onto the sides of the object being packaged.
According to a known method of wrapping waterproof packages, a top film is brought on top of the object being packaged from a roll of plastic film in two stages, so that the edge of the plastic film is first pulled to the centre of the object being packaged, from where the end of the plastic film is fetched and pulled across the wrapping station and cut to a fixed size while wrapping is interrupted, during the changeover of the products being packaged. The edges of the top film are then gripped and it is kept spread open above the object being packaged. When the first film layer has been wrapped, wrapping is interrupted for a short period during which the grip on the top film sheet is released and the edges of the top film are turned against the side surfaces of the object being packaged by means of air jets.
In a known wrapping machine, there is a top film feeding device and a drawing device, which move simultaneously in opposite directions. When wrapping is interrupted during the changeover of the products being packaged, the drawing device first pulls the edge of the top film to the centre of the object being packaged, from where the end of the top film is fetched and drawn across the wrapping station. The cutter cuts the top film to a fixed size. The wrapping machine comprises mechanical holders, which grip the edges of the top film and keep it spread open above the object being packaged. When the first plastic film layer has been wrapped, wrapping is interrupted for a short period and air jets turn the edges of the top film against the side surfaces of the object being packaged.
The wrapping machine described above, which relates to a known method of packaging by wrapping, is faster than earlier wrapping machines, but wrapping still has to be interrupted after the first film layer has been wrapped, when the top film sheet is released and its edges are turned against the side surfaces of the object being packaged.
The aim of the present invention is to provide a waterproof package according to a new method, which is more efficient than known methods. According to the method of packaging by wrapping, the wrapping of the object being packaged in the wrapping machine does not have to be interrupted in between. The wrapping at most slows down somewhat. Thus, a package provided with a top film can be made within almost the same time as an article without a top film is packaged. The capacity of the wrapping machine relating to the invention is in fact almost the same, regardless of whether a top film is used in the package or not.
By means of the invention, the top film is brought to the wrapping machine at a moment when wrapping is in any case interrupted, that is, when the packaged article is being removed from the wrapping station and the next object to be packaged is being brought to the wrapping station. It is also an essential feature that the forward movement of the objects being packaged and the already packaged articles on the conveyor track does not need to be interrupted or substantially slowed down.
The method of packaging by wrapping relating to the invention is characterised in
that the top film sheet brought to the wrapping station, to a position above the object being packaged, is turned upside down and placed on top of the object being packaged,
that during the first wrapping stage, the edges of the top film sheet are kept lifted up, after which the edges of the top film sheet are turned downwards and the second wrapping stage is carried out.
According to a preferred embodiment of the method relating to the invention
the top film is brought to the wrapping station, to a position above the object to be packaged, even before the object being packaged is changed over at the wrapping station,
and that during the changeover of the objects being packaged, the top film sheet is cut and fetched by turning it upside down and placing it on top of the object being packaged.
According to a second preferred embodiment of the method relating to the invention, the top film sheet is pressed onto the object being packaged by means of a pressing device while at the same time lifting the edges of the top film sheet upwards by means of the suction nozzles of the top film sheet carrier.
According to a third preferred embodiment of the method relating to the invention, the top film sheet is gripped by means of suction nozzles and the edges of the top film sheet are pressed downwards by means of blow nozzles.
According to a fourth preferred embodiment of the method relating to the invention, the same nozzle is used as a suction nozzle and a blow nozzle, the function of which nozzle is selected by connecting the nozzle duct either to the suction side of the fan or the pressure side of the fan.
The wrapping machine relating to the invention is characterised in
that the wrapping machine comprises a top film carrier for receiving the top film sheet on top of it,
that the top film carrier comprises a means for keeping the top film sheet attached to the top film carrier,
and that the top film carrier comprises a means for turning it upside down and for carrying the top film sheet under the top film sheet carrier and further on top of the article being packaged.
According to a preferred embodiment of the wrapping machine relating to the invention, the gripping means of the top film sheet carrier are suction nozzles and the pushing means are blow nozzles.
According to a second preferred embodiment of the wrapping machine relating to the invention
the nozzles of the top film sheet carrier are double acting, so that the same nozzles serve as both suction nozzles and blow nozzles,
the nozzles are connected to the fan by means of a change-over valve in such a way that the nozzles are suction nozzles when the change-over valve connects the nozzles to the suction side of the fan,
and the nozzles are blow nozzles when the change-over valve connects the nozzles to the pressure side of the fan.
According to a third preferred embodiment of the packaging machine relating to the invention, a pressing device is attached to the top film carrier of the wrapping machine for pressing the top film sheet onto the article being packaged.
According to a fourth preferred embodiment of the packaging machine relating to the invention, the top film carrier and pressing device of the wrapping machine are located above the rotation ring in such a way that the combined top film carrier and pressing device can be lifted by means of the rotation ring.